FIG. 1 shows the construction of a conventional plating apparatus. As shown in the drawing, the plating apparatus includes a plating bath 100. The plating bath 100 is provided with a main body 101 accommodating a plating solution Q, and a collecting vessel 102 for collecting the plating solution Q2 that overflows from the main body 101. A pump 103 transfers the plating solution Q2 collected in the collecting vessel 102 to a temperature regulator 104. The temperature regulator 104 regulates the plating solution Q2 to a predetermined temperature appropriate for plating. A filter 105 is provided for removing particles and the like from the plating solution Q2 as the solution is supplied to the main body 101. A flow meter 106 is provided for measuring the circulating flow of the plating solution.
With the construction described above, a substrate W such as a semiconductor wafer is retained in a retainer 108 within the main body 101, while an anode 107 is disposed also in the main body 101 and opposing the substrate W. A power source 109 supplies an electrical current between the substrate W and the anode 107 in order to plate the substrate W. When performing electroless plating, the plating bath 100 is not provided with the power source 109 or the anode 107. The plating process includes immersing the substrate W into the plating solution Q2.
When forming a plating film in fine channels or plugs for wiring formed in the substrate W or in opening portions of resist having poor wettability, sometimes the plating solution or preprocess solution cannot enter these fine openings, leaving air bubbles in the same. These bubbles can cause defects or omissions in the plating film.
In order to prevent such defects or omissions in the plating, a surface active agent has been added to the plating solution in conventional methods with the aim of lowering the surface tension of the plating solution to allow plating solution to enter the fine channels and plugs of the substrate and opening portions in the resist. However, lowering the surface tension of the plating solution increases the tendency of air bubbles to generate on the surface of the solution during circulation. Further, adding new surface active agent to the plating solution causes abnormalities to occur in the plating deposition and increases the amount of organic matter taken in by the plating film. Hence, this method can have an adverse effect on the properties of the plating film.